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Supplementary data:

Abstract

Petroleum impregnated sediments and massive sulfides have been found in two deeps of the northerns Red Sea. Biological marker distributions in extracts and polar fraction degradation products were analyzed in order to elucidate the source of the petroliferous material. Two organic phases could be distinguished according to their source and maturity.

The amounts of n-alkanes show a marked decrease with depth, whereas the concentrations of various branched and cyclic hydrocarbons increase, resulting in a humpof unresolvable compounds in a depth as shallow as 300 cm. Changes in concentrations and distributions of hopanoids in the Kebrit Deep sediments indicate a rapid increase of maturity with depth. The deepest core section (300 cm) and the masive sulfide reveal comparable maturation indices typical for mature oils.

By chemical degradation of the polar fractions a series of C40-isoprenoids was obtained, which reveals a considerable contribution from methanogenic and thermophilic archapbacteria to the immature organic matter. The data suggest that petroliferous material ofthermogenic origin migrates through the younger sequences, superimposes the autochthonous organic substances in the sediments and furthermore, forms asphaltic impregnations in the massive sulfides.